1. Field of the Disclosure
The present disclosure relates generally to electrophotographic imaging devices such as a printer or multifunction device having printing capability, and in particular to methods for controlling the transfer of toned black and color images during simplex printing.
2. Description of the Related Art
Color imaging devices contain two or more cartridges, each of which transfers a different color of toner to a media sheet as required to produce a full color copy of a toner image. A common imaging device includes four separate color cartridges—cyan, yellow, magenta, and black. Image formation for each of the four colors includes moving toner from a reservoir to an imaging unit where toned images, black or color are formed on photoconductive (PC) drums prior to transfer directly to a media sheet or to an intermediate transfer member (ITM) belt for subsequent transfer to a media sheet.
When printing black-only images, the color imaging units and, in particular, their PC drums, may run even when no color images are printed. This leads to additional wear on these PC drum and the toner particles. As such, two methods have been developed to reduce or eliminate such wearing by stopping the color imaging units while printing black-only images. In both methods, at least one motor is coupled to the color imaging units and another motor is coupled to the black imaging unit so that the black imaging unit can be run independently of the color imaging units. In the first method, the color motor is stopped and the ITM belt is allowed to slip between each nip formed between the color PC drums and a plurality of transfer rolls. The method only requires small gaps for each transition between black only and color printing. However, the charge on the surfaces of the color PC drums changes due to the movement of the ITM belt, requiring the color PC drums to be rotated occasionally while printing black pages such that the color PC drums will be fully recharged and cleaned at the end of every print job even if no color pages were printed. Rotation of the color PC drum also causes the color toners to be agitated as the color PC drum and toner agitators are coupled together and driven by the same motor. While this reduces color supply consumption, the color supplies may still need to be replaced due to wear on the PC drums even when no color pages were ever printed and where the color toner particles carry extra particulate additives (EPAs) the additional agitation may knock some of these EPAs from their carrier toner particles affecting toner performance.
In the second method, each transfer roll forming a nip with the color PC drums is retracted allowing the ITM belt to separate from the PC drums when printing black-only images and the color motor is stopped causing the color PC drums to stop rotating as well. When transitioning to printing color images, each retracted transfer roll is moved towards the color imaging units, moving the ITM belt to engage with the color PC drums and the color motors are restarted to rotate each of the color PC drums. This sequence reduces throughput when a print job contains both color and black-only images.
It would be advantageous to have a method of controlling the transfer of toned images that avoid the drawbacks of these two prior art methods.